Dynamics of single droplet impact on cylindrically-curved superheated surfaces

Abstract

Liquid droplet impact on superheated symmetric surfaces such as flat and spherical geometries has been extensively investigated in the past. However, the effect of a superheated asymmetric curvature on the collision dynamics remains unknown. In this study, experiments are performed to elucidate the thermo-hydrodynamic behavior of milli-metric water droplets impacting on superheated cylindrical surfaces having convex and concave profiles. These geometries offer an asymmetric zone for droplets to expand and retract. Mono-dispersed water droplets are impinged on convex and concave surfaces maintained in the temperature range of 125–290 °C. The impact Weber number is varied between 5 and 65 and droplet evolution is visualized using the high-speed imaging technique. It is observed that, droplet morphology and spreading characteristics are entirely different for convex and concave surfaces compared to a flat substrate due to momentum anisotropy. The maximum spread factor and residence time of the water droplet are significantly influenced by the impact Weber number while the surface superheat has negligible effect. Importantly, the asymmetric distribution of momentum facilitated 16% and 24% reduction in contact time for convex and concave surfaces respectively. The preferential extension of fluid in the azimuthal direction assisted by the gravity causes greater spreading of droplets on a convex surface. In contrary, these conditions enforced a reduction in contact time for droplets on a concave topography.